Variable displacement pump system

Abstract

A variable displacement pump has a swashplate controlled by a pair of pistons. A shuttle valve communicates the highest pressure pump workport to an operator-controlled displacement control valve. A pressure-responsive override valve is connected in series between the displacement control valve and the pistons. When an override pressure is achieved, the override valve blocks communication of the control valve with the pair of pistons and communicates the pump workports directly to the pistons for rapid destroking. A neutral bypass valve is formed out of a sleeve of the displacement control valve to bypass control pressure to sump when the displacement control valve is in neutral. A pressure-reducing valve limits the pressure acting on the stroke control valve to limit response rates and reduce erosion. The override valve includes orifices which, in intermediate positions, provide flow rate control of the fluid flow to the swashplate control pistons.

I claim: 
     
       1. A hydraulic system comprising: a variable displacment pump having high and low pressure workports and pressure-responsive displacement control means for controlling the displacement thereof;   an operator-controlled stroke control valve having a pair of outlets communicated with the displacement control means, a low pressure inlet connected to a reservoir, a high pressure inlet and a valve member movable to control communication between the inlets and outlets, thereby generating fluid pressure stroke control signals at the outlets, the valve member having a neutral position wherein the outlets and inlets are blocked, the stroke control valve comprising a spring-centered, operator-actuatable spool movable within a follower sleeve, the follower sleeve sensing swashplate position via a position feedback linkage, the neutral bypass valve being formed out of an extension of the follower sleeve; and   a neutral bypass valve for communicating the high pressure inlet to the reservoir when the valve member of the stroke control valve is in its neutral position.   
     
     
       2. The invention of claim 1, further comprising: a shuttle valve for communicating the high pressure workport to the high pressure inlet of the stroke control valve; and   a pressure-reducing valve coupled between the shuttle valve and the high pressure inlet for limiting the fluid pressure communicated to the high pressure inlet.   
     
     
       3. The invention of claim 1, further comprising: an override valve connected in series between the stroke control valve outputs and the displacement control means and movable in response to increased pump workport pressure from a normal position wherein stroke control signals from the stroke control valve are communicated to the stroke control means to an override position wherein pump workport pressures are communicated to the displacement control means to reduce pump displacement, the override valve having positions intermediate the normal and override positions wherein the stroke control signals are communicated to the stroke control means via orifices.   
     
     
       4. The invention of claim 3, wherein the override valve has a first intermediate position wherein the stroke control signals are communicated to the stroke control means via an orifice and wherein communication between the pump workports and the stroke control means is blocked, the override valve having a second intermediate position wherein the stroke control signals are communicated to the stroke control means via an orifice and wherein pump workport pressures are communicated to the displacment control means to reduce pump displacement. 
     
     
       5. The invention of claim 4, wherein the override valve further comprises: a further position wherein the stroke control signals are blocked from communicating with the stroke control means, wherein pump workport pressures are communicated to the displacement control means to reduce pump displacement and wherein pump workports are communicated with each other via an orifice.